1. Field of the Invention
The present invention relates to an optical-pickup feeding device used in an optical-disk apparatus for recording and reproducing information on a recording medium, such as a magneto-optical disk or an optical disk (hereinafter generically termed an “optical disk”).
2. Description of the Related Art
FIG. 8 is a plan view illustrating a conventional optical-pickup feeding device 20, and FIG. 9 is a cross-sectional view illustrating a principal portion of the device shown in FIG. 8. As shown in FIGS. 8 and 9, the conventional optical-pickup feeding device 20 generally adopts a lead screw mechanism as means for feeding an optical pickup 21 in the radial direction, i.e., in the horizontal direction in FIG. 8, of an optical disk 22.
That is, the optical-pickup feeding device 20 uses a feeding motor 24 (such as a stepping motor or a DC motor) fixed on a chassis 23, which serves as a substrate for assembly, as a driving source. A motor gear 28 fixed on the rotation shaft of the feeding motor 24 is connected to a driving gear 26 fixed on a driving guide shaft 25, via intermediate gears 27A and 27B.
In a typical conventional optical-pickup feeding device, in order to feed the optical pickup 21, three shafts, i.e., the driving guide shaft 25, a sub-guide shaft 29, and another sub-guide shaft, are used. In the device shown in FIG. 8, however, only two shafts, i.e., the driving guide shaft 25 and the sub-guide shaft 29, are used. End portions of these shafts are supported by guide-shaft supporting members 30a, 30b and 30c. This configuration is frequently used to support the optical pickup 21 is in optical-pickup feeding devices for MD's (mini-discs).
In the optical-pickup feeding device 20 shown in FIG. 8, a rack plate 31 for converting rotational movement into linear movement by meshed engagement with the driving guide shaft 25 is fixed on an end portion of the optical pickup 21. Accordingly, the optical pickup 21 is driven to a predetermined position in a radial direction in accordance with the angle of rotation of the driving guide shaft 25.
For example, when performing a reproducing operation, the optical disk 22 is driven by a spindle motor 32 at a predetermined revolution speed. At the same time, the optical pickup 21 is intermittently fed in a radial direction of the optical disk 22 by the feeding motor 24, that is, in a direction from the radial inside to the radial outside of the optical disk 22, while reading information written on tracks of the optical disk 22 by the optical pickup 21.
As shown in FIG. 9, when recording/reproducing information on/from the optical disk 22 mounted on a turntable 33, an objective lens 34 of the optical pickup 21 moves in tracking directions indicated by a two-headed arrow A and focusing directions indicated by a two-headed arrow B with respect to the optical disk 22, and a laser beam condensed on the objective lens 34 is incident upon and reflected from the substrate of the optical disk 22 at a predetermined tilt angle.
Accordingly, a gap L, shown in FIG. 9, between the objective lens 34 mounted in the optical pickup 21 and the surface of the substrate of the optical disk 22 must be within a predetermined tolerance throughout the operating range from the inner circumference to the outer circumference of the optical disk 22. The driving guide shaft 25 and the sub-guide shaft 29 guiding the optical pickup 21 are arranged parallel to each other and spread apart at a predetermined distance, and also are arranged parallel to the surface of the substrate of the optical disk 22.
In accordance with recent trends toward higher density in optical disks, the wavelength of laser light for recording and reproducing operations is becoming shorter, and a tolerance for error of the tilt angle of the laser beam is becoming more critical. As a result, higher accuracy is requested for the flatness of a chassis of a disk driving mechanism, accuracy in the relative vertical disposition of the shaft of a motor, and mounting of a guide shaft.
In order to solve such problems, tilt-adjusting optical-pickup feeding devices have been proposed. For example, as a method for adjusting the tilt angle by inclining a guide shaft, Japanese Patent Application Laid-Open (Kokai) No. 2000-11386 (2000) discloses a configuration in which both ends of a pair of guide shafts are supported by supporting members so as to be able to incline in a radial direction of the optical disk, and the guide shafts can be raised/lowered by elastically deforming a chassis on which the supporting members are provided.
However, such a configuration for supporting guide shafts requires a deceleration mechanism between a driving guide shaft and a motor, resulting in an increase in the number of components, higher production costs, and an increase in the occupied space, thereby causing impediments to reducing the size of the apparatus. Furthermore, since components of the deceleration mechanism cause increased variations in the load of the motor, the rating of the motor must be selected taking into consideration safety factors due to these variations.
In consideration of recent trends in feeding motors toward a smaller size and a higher torque, Japanese Patent Application Laid-Open (Kokai) No. 2000-339888 (2000) has proposed a method of directly driving an optical pickup, in which a lead screw is integrally formed on the rotation shaft of a motor, thereby omitting a conventional deceleration mechanism comprising a plurality of gears.
In this driving method, an optical pickup is supported by two guide shafts, and a motor including a lead screw is provided outside of the guide shafts. By adopting such a configuration, a lower cost is realized by omitting a deceleration mechanism comprising a plurality of gears and the like.
In such a driving method adopting a direct drive motor, although the tilt angle can be adjusted by the conventional approach of adjusting the inclination and the height of the guide shafts, two guide shafts are required. Since a lead screw and a motor are provided outside of the guide shafts, the external size of the optical-pickup feeding device increases, creating an impediment to reducing the size of the apparatus.
A configuration may also be adopted in which a direct drive motor integrated with a lead screw is adopted in the above-described configuration, in which the lead screw also operates as one of the guide shafts, as in the above-described MD type. However, since the conventional tilt adjusting method is devised for guide shafts that do not rotate, an appropriate tilt adjusting mechanism has not been devised in the above-described configuration. Furthermore, the above-described configuration is not conducive to assembling components.